1. Field of the Invention
Para-phenylene diamine (PPD) polymer is subject to an excessive and, until now, uncontrolled and unpredictable discoloration in isolation of the polymer from low-temperature solution polymerization. Discolored polymer yields discolored products and, even if the discoloration is not, of itself, unacceptable, discoloration of inconsistent degrees may well be unacceptable. This invention relates to a process for preparing PPD polymer having an improved color uniformity from run to run.
Description of the Prior Art
Prior to the present invention, it has been the practice to isolate PPD polymer from the solution polymerization media by washing in water without particular regard to the wash water or materials contained therein.
U.S. Pat. No. 4,308,374, issued Dec. 29, 1981 on the application of Vollbracht et al. discloses that poly-p-phenylene terephthalamide is isolated by mixing the reaction mixture with water or aqueous alkali. There is no mention of treatment to control discoloration in the polymer product.
U.S. Pat. Nos. 3,819,587 and 3,869,429, issued Jun. 25, 1974 and Mar. 4, 1975 on the applications of Kwolek and Blades, respectively, disclose that polyamides are isolated by being vigorously stirred with water and then filtered. Those patents, further, state that one of the washes may contain sodium carbonate or hydroxide. Neither patent is concerned with polymer discoloration.
Japanese Application Publication (Kokai) 58-40,306, published Mar. 9, 1983 discloses addition of alkali metal or ammonium salt of ethylenediaminetetraacetic acid to water-soluble acrylic copolymers to maintain the polymer water-solubility during pulverization. There is no mention of polymer discoloration.
U.S. Pat. No. 4,650,624, issued Mar. 17, 1987 on the application of Reinehr et al., discloses that EDTA can be used to increase the whiteness of dry spun acrylic fibers. The EDTA is added to the spinning solution and has nothing to do with production of the acrylic polymer.
U.S. Pat. No. 3,415,611, issued Dec. 10, 1968 on the application of Callahan et al., discloses that EDTA can be used to increase the whiteness of wet spun acrylonitrile fibers. The EDTA is added to the spinning solution or to spun fibers in the gel state and has nothing to do with production of the acrylonitrile polymer.